HYPERTENSION

Hypertension:
Persistent systolic pressure, more than 140 and diastolic more than 90 mm Hg. is regarded as hypertension.

The range of pressure increases with age.

Hypertension is the single most important risk factor in both coronary heart disease and cerebrovascular accidents.

It may also lead directly to congestive heart failure (hypertensive heart disease), renal failure and aortic dissection.

About 90% of hypertension is primary and idiopathic (essential).

The remaining is secondary and mostly related to renal disease or (less often) to renal artery stenosis (renovascular), endocrine abnormalities, vascular malformations, or neurogenic disorders.

Causes of hypertension:

I. Primary, essential, or idiopathic hypertension:

II. Secondary hypertension is due to the following causes:

1. Renal :

Acute glomerulonephritis ;

Chronic renal disease ;

Polycystic disease ;

Renal artery stenosis ;

Renal vasculitis ;

Renin-producing tumors ;

2. Endocrine:

Adrenocortical hyperfunction : Cushing syndrome, primary aldosteronism, congenital adrenal hyperplasia ;

Estrogen hormones : glucocorticoides, estrogen - including pregnancy and oral contraceptive, sympathomimetics, tyramine-containing foods, monoamine oxidase inhibitors ;

Pheochromocytoma ;

Achromegaly ;

Myxedema ;

Thyrotoxicosis ;

3. Cardiovascular :

Coarctation of aorta ;

Polyarteritis nodosa ;

Aortic insufficiency ;

Increased intravascular volume ;

Rigidity of the aorta ;

4. Neurologic:

Psychogenic ;

Increased intracranial pressure ;

Sleep apnea ;

Acute stress, including surgery ;


Regulation of Normal Blood Pressure :

Blood pressure is a complex trait that is determined by the interaction of multiple genetic and
environmental factors that regulate the relationship between cardiac output and total peripheral resistance.

1. Vasoconstriction increases vascular resistance.

Vasoconstrictors include angiotensin II, catecholamines, thromboxane, leukotrienes, and endothelin.

2. Vasodilators include kinins, prostaglandins, nitric oxide, and adenosine.

3. Regional autoregulation is also important, wherein increased blood flow leads to vasoconstriction and vice versa.

4. Cardiac output is regulated by blood volume (affected by sodium load, mineralocorticoids, and natriuretic factors), heart rate, stroke volume and contractility.


Mechanism of Essential Hypertension :

Although unknown, the cause of essential hypertension at the most elemental level must be related to a primary increase in cardiac output (e.g., reduced renal sodium excretion) or to an increase in peripheral resistance (e.g., owing to increased release of vasoconstrictor agents, to increased sensitivity of vascular smooth muscle cells, or to behavioural or neurogenic factors), or both (i.e., an increase in cardiac output and an increase in peripheral resistance).

In most patients, multiple defects probably contribute to the disease.

Abnormalities in the renal mechanisms that regulate blood pressure also may contribute to essential hypertension, including:

1. The renin-angiotensin system.

2. Sodium homeostasis.

3. Production of vasodepressor substances : It is implicated in the pathogenesis of hypertension in unilateral renal artery stenosis and renal disease.

For example, studies have suggested a propensity toward hypertension in individuals with specific molecular variants of the gene-encoding angiotensinogen, the physiologic substrate for renin.